title: Inhibition of coagulation and thrombin-induced platelet activities by a synthetic dodecapeptide modeled on the carboxy-terminus of hirudin.
abstract: A synthetic, tyrosine-sulfated, dodecapeptide (BG8865) modeled on residues 53-64 of hirudin was found to elevate the activated partial thromboplastin time (APTT), prothrombin time (PT), and thrombin time (TT) of human plasma in a dose-dependent manner. The most sensitive assay was the TT, which was prolonged 2 and 3 times control values at 2.2 and 4.1 micrograms/mL hirudin peptide, respectively. The sulfated dodecapeptide exhibited no dependency on antithrombin III as monitored by the APTT in the presence of sheep anti-human antithrombin III antibodies, and its activity was not neutralized by platelet releasates or platelet factor 4. In studies of thrombin-induced platelet activation, the hirudin peptide was found to block aggregation, serotonin release and thromboxane A2 generation. At thrombin concentrations of 0.25 U/mL, the IC50 (concentration resulting in 50% inhibition) for inhibition of platelet aggregation was 0.72 micrograms/mL peptide. Inhibition of TXA2 generation and serotonin release correlated closely with inhibition of aggregation. Using platelets from patients with clinically documented heparin-induced thrombocytopenia anticoagulant doses of heparin were found to induce platelet aggregation and thromboxane A2 generation. In sharp contrast, anticoagulant-equivalent doses of hirudin peptide had no effect on patient platelets, as evidenced by a lack of platelet aggregation and thromboxane A2 generation. These data provide compelling in vitro evidence that the hirudin peptide has several potential advantages over heparin, namely effective inhibition of thrombin-induced platelet activities, co-factor independence, insensitivity to endogenous heparin-neutralizing factors, and an apparent lack of direct or immune-mediated platelet stimulating properties.
authors.affiliation: Department of Hemostasis Research, Boston Veterans Administration Medical Center, MA.
authors.forename: J A
authors.initials: JA
authors.lastname: Jakubowski
authors.forename: J M
authors.initials: JM
authors.lastname: Maraganore
mesh_terms: D000595:Amino Acid Sequence; D000925:Anticoagulants; D001777:Blood Coagulation / Q000187:drug effects*; D001792:Blood Platelets / Q000187:drug effects*; D006493:Heparin / Q000494:pharmacology; D006629:Hirudins / Q000494:pharmacology*; D006801:Humans; D066298:In Vitro Techniques; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000494:pharmacology*; D010314:Partial Thromboplastin Time; D010446:Peptide Fragments; D010974:Platelet Aggregation / Q000187:drug effects*; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology; D013917:Thrombin / Q000494:pharmacology; D013921:Thrombocytopenia / Q000209:etiology; D013928:Thromboxane A2 / Q000096:biosynthesis
chemical_list: D000925:Anticoagulants; D006629:Hirudins; D009842:Oligopeptides; D010446:Peptide Fragments; D010975:Platelet Aggregation Inhibitors; C062510:hirugen; D013928:Thromboxane A2; D006493:Heparin; D013917:Thrombin